API collector: Optionally use UNIX sockets instead of TCP sockets, fix #1986

[monoidic]

The first commit adds the option of using UNIX sockets instead of TCP sockets for the API collector, which has performance benefits, and the second fixes an issue with the collector if the collector is reloaded.

[codecov-commenter]

Codecov Report

Merging #1987 (ecbd082) into develop (80e87ef) will increase coverage by 0.04%.
The diff coverage is 43.47%.

❗ Current head ecbd082 differs from pull request most recent head bac3d09. Consider uploading reports for the commit bac3d09 to get more accurate results

@@             Coverage Diff             @@
##           develop    #1987      +/-   ##
===========================================
+ Coverage    75.80%   75.85%   +0.04%     
===========================================
  Files          416      416              
  Lines        22228    22249      +21     
  Branches      2952     2942      -10     
===========================================
+ Hits         16850    16876      +26     
+ Misses        4698     4697       -1     
+ Partials       680      676       -4     

Impacted Files	Coverage Δ
intelmq/__init__.py	53.57% <ø> (ø)
...lmq/bin/intelmq_generate_misp_objects_templates.py	0.00% <ø> (ø)
intelmq/bin/intelmq_psql_initdb.py	65.57% <ø> (ø)
intelmq/bin/intelmqctl.py	12.88% <ø> (ø)
intelmq/bin/intelmqdump.py	18.30% <ø> (ø)
intelmq/bin/rewrite_config_files.py	0.00% <ø> (ø)
...ntelmq/bots/collectors/alienvault_otx/collector.py	42.42% <ø> (ø)
intelmq/bots/collectors/amqp/collector_amqp.py	73.07% <ø> (ø)
...q/bots/collectors/blueliv/collector_crimeserver.py	48.14% <ø> (ø)
...mq/bots/collectors/calidog/collector_certstream.py	46.15% <ø> (ø)
... and 399 more

[ghost]

Thanks again @monoidic !